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Tsirkin" To: Denis Plotnikov Subject: Re: [PATCH v2] vhost: make SET_VRING_ADDR, SET_FEATURES send replies Message-ID: <20210803105909-mutt-send-email-mst@kernel.org> References: <20210719142138.24543-1-den-plotnikov@yandex-team.ru> MIME-Version: 1.0 In-Reply-To: <20210719142138.24543-1-den-plotnikov@yandex-team.ru> Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=mst@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Received-SPF: pass client-ip=216.205.24.124; envelope-from=mst@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -34 X-Spam_score: -3.5 X-Spam_bar: --- X-Spam_report: (-3.5 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.699, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: qemu-devel@nongnu.org, yc-core@yandex-team.ru Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Mon, Jul 19, 2021 at 05:21:38PM +0300, Denis Plotnikov wrote: > On vhost-user-blk migration, qemu normally sends a number of commands > to enable logging if VHOST_USER_PROTOCOL_F_LOG_SHMFD is negotiated. > Qemu sends VHOST_USER_SET_FEATURES to enable buffers logging and > VHOST_USER_SET_VRING_ADDR per each started ring to enable "used ring" > data logging. > The issue is that qemu doesn't wait for reply from the vhost daemon > for these commands which may result in races between qemu expectation > of logging starting and actual login starting in vhost daemon. > > The race can appear as follows: on migration setup, qemu enables dirty page > logging by sending VHOST_USER_SET_FEATURES. The command doesn't arrive to a > vhost-user-blk daemon immediately and the daemon needs some time to turn the > logging on internally. If qemu doesn't wait for reply, after sending the > command, qemu may start migrate memory pages to a destination. At this time, > the logging may not be actually turned on in the daemon but some guest pages, > which the daemon is about to write to, may have already been transferred > without logging to the destination. Since the logging wasn't turned on, > those pages won't be transferred again as dirty. So we may end up with > corrupted data on the destination. > The same scenario is applicable for "used ring" data logging, which is > turned on with VHOST_USER_SET_VRING_ADDR command. > > To resolve this issue, this patch makes qemu wait for the commands result > explicilty if VHOST_USER_PROTOCOL_F_REPLY_ACK is negotiated and > logging is enabled. > > Signed-off-by: Denis Plotnikov > --- > v1 -> v2: > * send reply only when logging is enabled [mst] > > v0 -> v1: > * send reply for SET_VRING_ADDR, SET_FEATURES only [mst] > > hw/virtio/vhost-user.c | 37 ++++++++++++++++++++++++++++++++++--- > 1 file changed, 34 insertions(+), 3 deletions(-) > > diff --git a/hw/virtio/vhost-user.c b/hw/virtio/vhost-user.c > index ee57abe04526..133588b3961e 100644 > --- a/hw/virtio/vhost-user.c > +++ b/hw/virtio/vhost-user.c > @@ -1095,6 +1095,11 @@ static int vhost_user_set_mem_table(struct vhost_dev *dev, > return 0; > } > > +static bool log_enabled(uint64_t features) > +{ > + return !!(features & (0x1ULL << VHOST_F_LOG_ALL)); > +} > + > static int vhost_user_set_vring_addr(struct vhost_dev *dev, > struct vhost_vring_addr *addr) > { > @@ -1105,10 +1110,21 @@ static int vhost_user_set_vring_addr(struct vhost_dev *dev, > .hdr.size = sizeof(msg.payload.addr), > }; > > + bool reply_supported = virtio_has_feature(dev->protocol_features, > + VHOST_USER_PROTOCOL_F_REPLY_ACK); > + > + if (reply_supported && log_enabled(msg.hdr.flags)) { > + msg.hdr.flags |= VHOST_USER_NEED_REPLY_MASK; > + } > + > if (vhost_user_write(dev, &msg, NULL, 0) < 0) { > return -1; > } > > + if (msg.hdr.flags & VHOST_USER_NEED_REPLY_MASK) { > + return process_message_reply(dev, &msg); > + } > + > return 0; > } > OK this is good, but the problem is that we then still have a race if VHOST_USER_PROTOCOL_F_REPLY_ACK is not set. Bummer. Let's send VHOST_USER_GET_FEATURES in this case to flush out outstanding messages? > @@ -1288,7 +1304,8 @@ static int vhost_user_set_vring_call(struct vhost_dev *dev, > return vhost_set_vring_file(dev, VHOST_USER_SET_VRING_CALL, file); > } > > -static int vhost_user_set_u64(struct vhost_dev *dev, int request, uint64_t u64) > +static int vhost_user_set_u64(struct vhost_dev *dev, int request, uint64_t u64, > + bool need_reply) > { > VhostUserMsg msg = { > .hdr.request = request, > @@ -1297,23 +1314,37 @@ static int vhost_user_set_u64(struct vhost_dev *dev, int request, uint64_t u64) > .hdr.size = sizeof(msg.payload.u64), > }; > > + if (need_reply) { > + bool reply_supported = virtio_has_feature(dev->protocol_features, > + VHOST_USER_PROTOCOL_F_REPLY_ACK); > + if (reply_supported) { > + msg.hdr.flags |= VHOST_USER_NEED_REPLY_MASK; > + } > + } > + > if (vhost_user_write(dev, &msg, NULL, 0) < 0) { > return -1; > } > > + if (msg.hdr.flags & VHOST_USER_NEED_REPLY_MASK) { > + return process_message_reply(dev, &msg); > + } > + > return 0; > } > > static int vhost_user_set_features(struct vhost_dev *dev, > uint64_t features) > { > - return vhost_user_set_u64(dev, VHOST_USER_SET_FEATURES, features); > + return vhost_user_set_u64(dev, VHOST_USER_SET_FEATURES, features, > + log_enabled(features)); > } > > static int vhost_user_set_protocol_features(struct vhost_dev *dev, > uint64_t features) > { > - return vhost_user_set_u64(dev, VHOST_USER_SET_PROTOCOL_FEATURES, features); > + return vhost_user_set_u64(dev, VHOST_USER_SET_PROTOCOL_FEATURES, features, > + false); > } > > static int vhost_user_get_u64(struct vhost_dev *dev, int request, uint64_t *u64) > -- > 2.25.1